P2BADPowertrain
Powertrain · SAE
NOx Emissions Too High (SCR/AdBlue)
Meaning
Measured NOx at the exhaust exceeds the allowed limit. The SCR system cannot reduce the nitrogen oxides sufficiently.
Common causes
- Dosing fault in the SCR/AdBlue system
- Poor-quality AdBlue or the wrong fluid
- Faulty or inaccurate NOx sensor
- EGR (exhaust gas recirculation) fault
- Exhaust leak upstream of the NOx sensor
- Aged SCR catalyst or blocked dosing injector
Symptoms
- Check-engine light, emissions-system message
- Reduced power
- Restart-limit countdown
- Failed emissions check
- Abnormal AdBlue consumption
Severity
Moderate to high: emissions are out of compliance; the vehicle may limit performance and restarts.
What to do
- Read live data for the upstream/downstream NOx sensors and AdBlue dosing
- Check AdBlue quality and level and rule out the wrong fluid
- Inspect the EGR and look for an exhaust leak upstream of the NOx sensor
- Replace the faulty NOx sensor or restore correct SCR/AdBlue dosing